The effect of hydronium ions on the structure of phospholipid membranes.

This work seeks to identify the mechanisms by which hydronium ions (HO) modulate the structure of phospholipid bilayers by studying the interactions of HO with phospholipids at the molecular level. For this, we carried out multiple microsecond-long unrestrained molecular dynamics (MD) simulations of a POPC bilayer at different HO concentrations. The results show that HO accumulates at the membrane surface where it displaces water and forms strong and long-lived hydrogen bonds with the phosphate and carbonyl oxygens in phospholipids. This results in a concentration-dependent reduction of the area per lipid and an increase in bilayer thickness. This study provides an important molecular-level insight into the mechanism of how HO modulates the structure of biological membranes and is a critical step towards a better understanding of the effect of low pH on mammalian and bacterial membranes.